1. Field of the Invention
The present invention relates to processing of slurries. More particularly, the present invention relates to apparatus and methods for processing slurries.
2. The Prior Art
Many processes in industries such as farming, the food and beverage industry and others, involve the handling of slurries including mixtures of solids and liquids. In a large number of these processes, it becomes necessary at some point to separate the solid components of the slurries from the liquid components of the slurries. A non-exhaustive list of examples of slurries include manure, beer and wine sludge, nut and grain hulls and other food products.
There are numerous reasons to separate out liquid components of slurries. Such purposes include, but are not limited to, waste water processing, clean water recovery, weight reduction prior to hauling solid waste components of a process to reduce transportation costs.
One particular application of the need for separation of solids and liquids from slurries is found in dairy farming. On dairy farms, dairy cows eat and walk on concrete flush lanes. While in these lanes, the cows excrete solid and liquid waste, approximately 15 to 20 gallons of solid waste per cow per day. The solid waste is a valuable commodity and is used for fertilizing as well as creating bedding for cows. Thus, dairy farms pump water from large storage lagoons into the dairy cow flush lanes in order to flush the lanes and collect the solid and liquid waste, in a storage pit from which it is mixed and pumped over a screen separator to remove the solids from the water.
It is known in the art to pump the flushed water, that is water that has already been flushed down the dairy cow flush lane, to a solid waste separator. One known method of separating the solid waste is to use a metal screen filter, onto which the flushed water is pumped. The water passes through the metal screen while a percentage of the solid waste remains on the top surface of the metal screen filter. The solid waste slides off the screen onto a solid waste storage slab. The solid waste then can be removed from the storage slab and used for fertilizer, or it may be further processed into a compost heap to make a more valuable form of fertilizer. Once a percentage of solid waste is removed from the flushed water, the flushed water is drained into a storage lagoon. The flush cycle repeats by pumping water from the storage lagoons down the dairy cow flush lanes.
Given that a typical large dairy farming operation may have 5,000 dairy cows, and 35 dairy cow flush lanes. A typical flush pump used in such an operation has a 2200 gallon per minute capacity. Usually, each dairy cow flush lane has a flush lane valve, which opens for each lane for 5 minutes at a time during each flush cycle. Thus, 2,200 gallons per minute is flushed down each flush lane for 5 minutes, thereby using 11,000 gallons per flush cycle per lane. Since a typical dairy farm has approximately 35 flush lanes, and a typical dairy farmer flushes at least 4 times a day, and each cow produces 15 gallons of waste per day, it follows that about 1,615,000 gallons of water per day must be pumped and processed through the solid waste separator before the water is redirected back to the storage lagoon.
One prior-art system is described in U.S. Pat. No. 6,531,057, issued to the same inventor as the present invention. A solid waste separator is coupled to a conveyor system. The conveyor system moves the solid waste from the solid waste separator up a screen conveyor 320. The conveyor moves the solid waste into a spring loaded tunnel press, which removes excess water from the solid waste. The excess water drains to either the process pit or the storage lagoon through pipe 350. The solid waste drops and stacks into a solid waste stack 340.
A problem in the prior art dairy cow flush lane system is that the flushed water drained from the solid waste separator often contains a high percentage of solid waste. This is due to the fact that the more diluted the solid waste in the water is, the less efficient the metal screen filter is in removing solid waste from the flushed water. Water that contains 0.5% solid waste does not filter as efficiently as water that contains 2% solid waste. This results in dirty water being drained into the storage lagoon. After each flush cycle, the storage lagoon collects more solid waste. Methane gas buildup occurs in the storage lagoon, and the gas is then released into the atmosphere, causing pollution. The water in the storage lagoon is also used to fertilize fields, once the storage lagoon becomes too dirty, the fields and crops can be damaged by the high content of solid waste in the water. Also, as the storage lagoon water contains more solid waste, it becomes more difficult to properly flush the dairy cow flush lanes with the storage lagoon water that already has high levels of solid waste material.
Another drawback to the typical dairy cow flush lane system, is that for every gallon pumped down the flush lane, that same amount of water must first be pumped through a solid waste separator pump, plus any waste collected to the solid waste separator, before being drained back to the storage lagoon. This means that a solid waste separator pump must run for long periods of time due to the high volume of flushed water used and solid waste resulting from flushing the dairy cow flush lanes. Because the solid waste separator pump runs for such a long period of time, there are associated high energy costs to run the pump as well as higher maintenance and repair cost.
It is known to pass a slurry over an inclined slot sieve to remove liquid from a slurry as in the above-described prior-art system. Gravity causes the slurry to courses over the slot sieve. As the slurry descends, the water or other liquid contained in the slurry passes through the slots to a channel that captures the liquid, while and the solids continue down the top surface o the sieve. At the bottom of the sieve, the solids pile up and cascades over a lower edge of the sieve. A removal mechanism, such as a conveyor belt running parallel to the bottom edge of the sieve assembly, may be used to carry away the solids to allow the liquid separation process to be continuous.
A significant problem in the prior art slurry separation systems is that the slots in the sieve become clogged with solid matter, which must be removed or else the operation of the slurry separation system becomes less efficient, with the result that the solid component of the slurry retains an increasing amount of the liquid as the slots become progressively more clogged.
The clogging of the slots requires maintenance measures to be performed to keep the process running satisfactorily. In some instances, a worker is sent to manually hose down the slot sieve to dislodge the solid matter that has accumulated in the slots. Such manual maintenance procedures are labor intensive are generally not completely satisfactory to maintain the system running at top efficiency.
In some systems attempts have been made to automate this maintenance somewhat. FIG. 1 shows a portion of a typical slot sieve separator including a typical arrangement for dislodging solids from the slot sieve. Separator assembly 10 includes an inclined housing 12 onto which one or more slot sieve sections 14 are mounted to an inclined slot sieve in a slurry separation system. A slurry (not shown) is pumped to the top of the assembly and allowed to run down the slot sieve 14. The slots are spaced apart by a distance that allows the liquid component of the slurry to pass through them into a channel 16 disposed below the slots where it runs to the bottom of the assembly and is carried away by pipes or conduits. The solid component of the slurry passes down the sieve to the bottom, where it may be carried away by means such as a conveyor belt (not shown).
A flexible hose 18 having a nozzle 20 at its end is mounted above the sieve along a track 22 near the top of the separator assembly 10 and is provided with a driving mechanism (not shown) that allows it to be moved horizontally over substantially the entire width of the assembly 10 to direct a stream of water or other liquid at the face of the slots sieve. This method is described in the aforementioned U.S. Pat. No. 6,531,057.
While this arrangement has proved to be superior to reliance on manual hosing maintenance operations, there are several drawbacks to this method including that the water stream is only directed along a small horizontal portion over the entire length of the separator assembly 10. There thus remains room for improvement of processes such as shown in FIG. 1.